<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <style>
      #main {
        position: fixed;
        left: 50%;
        right: 0;
        top: 0;
        bottom: 0;
        background-color: #ff0000;
      }
    </style>
  </head>
  <body>
    <div id="main"></div>
  </body>
</html>
